function doAdd(){
  $(".content-one").click(function(){
    $(".content-one").css("background-image","none").css("color","black");
    $(this).css("background-image", "linear-gradient(-45deg, #4BC0FF 0%, #4CA9FF 98%, #4CA9FF 100%)").css("color","#FFFFFF");
    $(".child").css("color","#999999");
    $(this).next().css("color", "#4BBEFF");
  })
}
doAdd();